Galfenol – A New Class of Magnetostrictive MaterialsGALFENOL PUBLIC RELEASE v.7

Prepared by Eric Summers, Vice President & Chief Scientist

2ETREMA Products, Inc.

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Motivation

Magnetostrictive alloys must exist that exhibit the optimum combination of good magnetostriction and mechanical robustness

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Magnetostriction vs. Composition (single crystals)

Fe1-xGa(0.15 ≤ x ≤ 0.20)

Single crystal data from:

Magnetic Materials Group –

Carderock Division, Naval

Surface Warfare Center

(NSWC)

ETREMA’s efforts have focused

on the first magnetostrictive

peak between 15 at% Ga and

20 at% Ga

Nominal Ga content in ETREMA

produced Galfenol is 18.4 at%

ETREMA produces coarse-

grained polycrystalline samples0 5 10 15 20 25 30 35 40

0

50

100

150

200

250

300

350

400

450

Furnace CooledQuenchedDirectionally Solidified (Unannealed)Quenched in BrineFurnace Cooled, Multi-phase

Fe100-xGax

H = 15 kOe

Ma

gn

eto

str

ictio

n, p

pm

at% Ga Content (x)

4ETREMA Products, Inc.

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Galfenol Production Method

Advanced Bridgman Process

Directional solidification process

Primary composition centers on 18.4 at% Ga, nominal

Other compositions available upon request

Standard diameter produced = 24 mm

30 mm in development

Typical length produced = 250 mm

This is followed by machining of requested component geometry

Photo of Galfenol being produced via Bridgman Process

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Typical Properties

Saturation Strain 200 – 250 ppm at 48 MPa applied compressive load

Piezomagnetic Constant, d33 15 – 30 nm/A, lower values at larger stresses

Saturating Magnetic Field 100 – 250 Oe, value depends upon stress applied with larger

stresses requiring high magnetic fields to reach saturation

Saturation Magnetic Flux Density 1.5 Tesla

Magnetic Permeability, μr 75 – 100, lower values at larger stresses

Coercivity, Hc 10 Oe

Hysteresis (major loop) 1000 J/m3

Curie Temp. ≈ 950 K

Density 7800 kg/m3

Hard Young’s Modulus 75 GPa

Soft Young’s Modulus ≈ 40 GPa, achieved during magnetic moment rotation

Tensile Strength ≈ 350 MPa

Elongation ≈ 1%

Typical properties of polycrystalline Galfenol (Fe81.6Ga18.4)

As-grown material via Bridgman Process

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Typical as-grown Strain-H Curves(under various compressive loads)

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Typical as-grown B-H Curves(under various compressive loads)

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Villari Effect for Galfenol Sensing/Energy Harvesting

Compressive stress vs. flux density

~1 T

~70 MPa

Graph from testing completed by Dr. Toshiyuki Ueno, Kanazawa University, Japan

Test results from a typical Galfenol sample

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Less magnetic field required to reach saturation

Larger pre-stresses maybe necessary

Larger saturation flux density

Higher permeability

Less hysteresis

Comparison to Terfenol-D

Strain vs. Magnetic Field Flux Density vs. Magnetic Field

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Galfenol Characteristics

Galfenol that has been

milled and lathed

Galfenol plate TIG welded to a

steel cylinder

Photos shown are of 18.4 at% Ga samples, nominal composition

Material can be machined using conventional machining techniques; such as mills, lathes, and EDM’s

Material can be welded using TIG welding techniques

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Fabricated Galfenol Part Examples

Galfenol

Laminated and machined threads

Machined and laminated “C”-cores

Forged and machined horseshoes

Laminated and milled stack

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Stress Annealing of Galfenol alloys

Stress annealing process builds in a compressive stress into the Galfenol sample (referred to as an ‘uniaxial anisotropy’)

Result: full magnetostrictive performance without application of an external compressive stress mechanism

Good magnetostrictive performance under tensile loads

Tension limitation around 50 MPa

ETREMA has successfully stress annealed Galfenol alloys from 15 at% to 18.4 at% Ga

Recent processing advancements have doubled the length that can be stress annealed to 250 mm

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Typical stress-annealed Strain-H Curves (under various compressive loads)

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Typical stress-annealed B-H Curves (under various compressive loads)

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Energy Harvesting Possibilities

Galfenol can be designed into various energy harvesting

configurations

Large half-power bandwidths exhibited when directly coupled to

large forces or displacements Examples shown below for a lab prototype Galfenol energy harvester

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Conclusions

Galfenol currently produced using an Advanced Bridgman directional solidification method

Can use conventional machining and welding techniques to form a variety of shapes

Galfenol can be stress annealed to operate without an applied compressive load and achieve 100% of it’s magnetostrictive performance

Galfenol’s mechanical robustness allow it to be used in a displacement (force) based energy harvester that exhibits large half-power bandwidths

ETREMA is actively searching for collaborators to help advance and integrate Galfenol technologies into next-generation products

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Notice of Disclaimer

Information presented here-in does not grant patent right, copyright, or intellectual property rights of ETREMA Products, Inc. (EPI) or that of third parties. EPI disclaims all liability arising out of using information in this presentation for any case of patent right, copyright, or intellectual property rights of third parties.

Do not duplicate in part or in its entirety without written permission from EPI.

The information presented and its contents are subject to change without notice; specific technical characteristics are subject to consultation and agreement.

Please inquire about specific applications of Galfenol material to ensure the likelihood of success.